Stress, strain, and microstructure of sputter-deposited Mo thin films

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Abstract
Mo thin films were deposited on glass substrates using direct‐current (dc) planar magnetron sputtering. Mechanical determination of the internal stresses, using the bending‐beam technique, yielded typical compressive‐to‐tensile stress transition curves with increasing working‐gas pressure. The microstructure of the compressively stressed films consists of tightly packed columns, whereas in the tensily stressed films the development of a void network structure surrounding the columnar grains is observed. At elevated working‐gas pressures the onset of microcolumns is observed in the initial stage of film growth. Determination of lattice strains by x‐ray diffraction (XRD), utilizing the sin2 ψ method, encounters more difficulties than the more straightforward stress determination by the bending‐beam method. Here special attention is focused on deviations from linear dependence of dψ with sin2 ψ along with asymmetry of XRD line profiles that results from stress‐depth profiles as well as lateral stress distributions in the tensily stressed films. These anomalies and the discrepancy between bending‐beam stresses and XRD lattice strains, observed for high working‐gas pressures, can be interpreted in terms of microstructural features revealed by cross‐sectional transmission electron microscopy.

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